The invention relates to an apparatus which generates ionizing radiation. Apparatus of this kind can, for example, be electron microscopes or X-ray tubes or other electron beam or particle beam apparatus.
British patent publication 2,007,480 discloses a radiation shield for electrical equipment wherein the production of radiation is associated with high electrical gradients. In this publication, an X-ray tube or an ion accelerator are known which include a tube manufactured from lead or an epoxy-resin mixture which contains another heavy metal greatly absorbing ionizing radiation. The tube accommodates the electrodes for accelerating the particle beam. Alternatively, it is suggested that the conventional X-ray tube be surrounded by a protective shield of a corresponding epoxy-resin mixture. In this way, a reliable X-ray protection is ensured.
In a protective shield made of an epoxy-resin mixture containing lead, the same problems occur at breakthroughs as in protective shields of lead. These breakthroughs are, for example, for manipulators such as diaphragm exchangers or sample manipulators. More specifically, these same problems are that it is almost impossible to make the protective shield tight against escaping X-ray radiation in the region of a manipulator. The same applies when the tube itself, which carries the components such as the electrodes, comprises an epoxy-resin mixture containing lead. In the last case, it is noted that the epoxy-resin mixture, as a rule, does not have the stiffness and strength which are especially required in electron microscopes for the accommodation of electron-optical components.
It is an object of the invention to provide a column for an apparatus which generates ionizing radiation wherein the column can be configured tight against escaping X-ray radiation and has the required stiffness and strength for accommodating particle-optical components.
In the apparatus of the invention, ionizing radiation is generated. The apparatus includes: a tube having an inner surface defining an interior space; particle-optical components supported in the interior space by the tube; a layer of cured epoxy-resin mixture containing a heavy metal and surrounding the tube on the outside thereof; and, the layer of cured epoxy-resin mixture defining a unit adhering to the tube.
The apparatus of the invention includes a column which has a sandwich-like configuration. In a first embodiment, the tube, which supports the particle-optical components, is surrounded on the outside by a layer which comprises an epoxy-resin mixture containing a heavy metal. The tube and the layer of epoxy-mixture are glued to each other so that they define a static unit.
In an alternate embodiment, the column includes an outer tube and an inner tube disposed within the outer tube. The outer and inner tubes conjointly define an intermediate space which is filled with an epoxy-resin mixture containing a heavy metal. In this embodiment too, the epoxy resin adheres to the inner tube and/or the outer tube.
The following heavy metals, which are suitable and absorb sufficient X-ray radiation, are especially metals having an atomic number greater than 75 such as tungsten and/or lead or a chemical compound thereof such as their oxides.
The desired adhesion of the epoxy-resin mixture to the tube or to the inner and/or outer tube takes place, as a rule, automatically when the epoxy-resin mixture is poured into the intermediate space between the inner and outer tubes or the intermediate space between the tube and the casting mold, which surrounds the tube, is filled with the epoxy-resin mixture.
The hardened epoxy-resin mixture is included in the force flow between the outer tube and the inner tube; that is, the forces, which are applied by the components (mounted on the inner tube), are transmitted via the intermediate space, which is filled with the epoxy-resin mixture, to the outer tube. Likewise, in the embodiment having only one tube, the outer layer of the epoxy-resin mixture is included in the force flow because the forces, which are applied by the mounted components, are transmitted via the layer of epoxy-resin mixture to the tube. These components include manipulators or aperture changers.
Purposefully, at least one of the tubes is made of steel or a steel alloy in order to ensure the required stiffness and strength. It is, however, especially advantageous when the inner tube as well as the outer tube are made of metal, for example, steel, because the sandwich-like configuration then additionally effects an efficient shielding of electrical and magnetic fields.
The column of the apparatus can comprise a plurality of tube segments or inner tube segments and outer tube segments which are arranged one behind the other in the axial direction, that is, in the direction of the axes of the inner and outer tubes. At the connecting locations at which the tube segments abut one another, mutually engaging cutouts arid projections are provided so that the intermediate spaces, which are filled with the epoxy-resin mixture or the epoxy-resin layers of the stacked segments, overlap each other. In this way, it is possible that the entire apparatus is assembled of several premanufactured component pieces without X-ray passing holes occurring at the connecting locations, that is, locations at which X-ray radiation can escape out of the outer tube into the ambient.
The column can have one or several openings in the radial direction with a manipulator or diaphragm holder accommodated therein. The manipulator should have a support structure which is likewise provided with a layer of an epoxy-resin mixture containing a heavy metal. The thickness of the layer is so selected that the layer of the epoxy-resin mixture overlaps the edge of the breakout through the tube.
The support structure of the manipulator or of the aperture holder is configured to be stepped or conical with the transverse dimension increasing toward the outside. In this way, it is easier to achieve that the epoxy-resin mixture of the manipulator or of the aperture diaphragm and the epoxy-resin mixture of the column overlap at least at a transition region so that a configuration is ensured which is tight against X-ray radiation also at the breakout for the manipulator or diaphragm holder.
Components such as operator-controlled knobs are arranged in the radial direction of the column and are on the manipulator or diaphragm holder. It is further advantageous that these components are filled out with an epoxy-resin mixture having a heavy metal.